1. Technical Field
The present invention relates generally to broadcast transmissions and, in particular, to a method and system for preventing unauthorized playback of broadcasted digital data streams.
2. Background Description
In the current environment of networks and with the proliferation of digital and digitized multimedia content which may be distributed over such networks, a key issue is copyright protection. Copyright protection is the ability to prevent or deter the proliferation of unauthorized copies of copyrighted works.
A significant problem in the digital world is that an unlimited number of perfect copies may be made from any piece of digital or digitized content. A perfect copy means that if the original is comprised of a given stream of numbers, then the copy matches the original, exactly, for each number in the stream. Thus, there is no degradation of the original signal during the copy operation. In an analog copy, random noise is always introduced, which degrades the copied signal.
The act of making unlicensed copies of some content, whether digital or analog, audio, video, software of other, is generally referred to as piracy. Piracy has been committed for the purpose of either profit (e.g., selling such unlicensed copies) or to procure a copy of the content for personal use without having to pay for it. The definition of piracy has also been extended to cover the situation when copies of protected materials are distributed without profit. The problem of piracy is worse for digital content. This is because once a pirate finds a way to defeat any existing protection schemes implemented to guard against piracy, he may then make an unlimited number of copies without any degradation in the quality of the copies. On the other hand, in the analog world, there is generally a degradation in the content (signal) with each successive copy, thereby imposing a sort of natural limit on the volume of piracy.
In general, three approaches have been implemented to protect copyrights. They are encryption (the process of encoding data for security purposes), copy protection, and content extensions. Copy protection and content extensions generally apply to the digital world, while a scheme related to encryption, typically referred to gas scrambling, may be applied to an analog signal. This is commonly found in analog cable systems.
Encryption scrambles the content which, once it has been encrypted, cannot be used until it is decrypted or unscrambled. For example, encrypted video may appear as random patterns on a screen. The principle of encryption is that you are free to make as many copies as you desire, but you cannot view anything which is coherent until you decrypt it using a special key. The key is obtained upon paying for the protected content. However, encryption schemes are not without deficiency. For example, a pirate could buy a single, encrypted copy of some content, which he is entitled to decrypt. Then, the pirate could make unlimited copies of the decrypted copy.
Copy protection includes various methods by which a software engineer can write software so as to determine if it has been copied and, if so, to deactivate itself. However, this scheme has been pretty much abandoned since such methods have historically been circumvented.
Content extension refers to any system which attaches some extra information to the original content which indicates whether or not a copy may be made. A software or hardware system must be specifically built around this scheme to recognize the additional information and interpret it in an appropriate manner. Such software or hardware is generally referred to as being xe2x80x9ccompliantxe2x80x9d with the scheme. An example of a content extension system is the Serial Copyright Management System embedded in Digital Audio Tape (DAT) hardware. Under this system, additional information is stored on the disc immediately preceding each track of audio content which indicates whether or not it can be copied. The hardware reads this information and uses is accordingly.
Information, such as that added in a content extension scheme, may be incorporated into content to be protected through the use of a watermark. The idea behind a watermark is that it should not be able to be removed from the item it corresponds to without actually destroying that item. In the digital domain, a digital watermark is a imperceptible or preferably invisible identification code that is permanently embedded in the data and, thus, remains present within the data after any decryption process. Unfortunately, copyright protection techniques implementing watermarking have also been historically defeated. For example, many techniques implementing watermarking have been defeated by a technique referred to as averaging. Moreover, some watermarking techniques may be defeated by simply ignoring the watermark (i.e., by not complying with the watermarking scheme).
The above problems are compounded by the proliferation of digital devices. For example, digital televisions (e.g., high definition television (HDTV)) are now being developed and marketed which enable playback of input digital signals, as compared to conventional televisions which receive an analog input signal. FIG. 1 is a block diagram of a conventional digital television 100. The television 100 includes: a receiver 102; a conditional access (CA) module 104; and a bus 106 operatively connecting receiver 102 and CA module 104.
In operation, a signal is extracted from the airwaves via an antenna 108 and input to receiver 102. The receiver 102 forwards the signal to CA module 104 which decrypts the signal and then forwards the decrypted signal back to receiver 102. Since bus 106 could be potentially tapped, a non-compliant recorder/player could masquerade as receiver 102 and make a bit-for-bit copy of, for example, a pay-per-view program, on this bus. Thus, the bit-for-bit copy would be made after the signal has been decrypted by CA module 104. The non-compliant recorder/player could then masquerade as CA module 104 so that the illicitly recorded program is displayed on receiver 102. In such a case, receiver 102 is sent decrypted content (by the non-compliant recorder/player) and assumes the content is legitimate. Additionally, the recording can be transmitted to a network of non-compliant playback devices.
Thus, it would be desirable and highly advantageous to have a method and system for preventing unauthorized playback of broadcasted data streams such as digital video streams.
The present invention is directed to a method and system for preventing unauthorized playback of digital data streams.
In one aspect of the present invention, a method for preventing unauthorized playback of digital data streams comprises the steps of:
embedding a watermark in a digital data stream;
encrypting the digital data stream having the embedded watermark;
broadcasting the encrypted digital data stream with a ticket;
receiving the encrypted digital data stream and the ticket;
saving the ticket and providing the encrypted digital data stream to a decryption device to decrypt the digital data stream;
receiving the decrypted digital data stream from the decryption device;
extracting the.watermark from the decrypted digital data stream;
applying a one-way cryptographic hashing function to the saved ticket;
comparing the hashed ticket to the extracted watermark; and
preventing playback of the digital data stream, when the hashed ticket does not match the extracted watermark.
In another aspect of the present invention, a system for preventing unauthorized playback of broadcasted digital data streams comprises:
a bus;
a conditional access module operatively coupled to the bus configured for decrypting encrypted digital data streams;
a receiver operatively coupled to the bus configured for receiving an encrypted digital data stream having a watermark embedded therein and a ticket, saving the ticket, providing the encrypted digital data stream to the conditional access module, and receiving a decrypted digital data stream from the conditional access module, the receiver comprising:
an extractor configured for extracting the watermark from the decrypted digital data stream;
a hashing module configured for applying a one-way cryptographic hashing function to the saved ticket; and
a comparison.module configured for comparing the hashed ticket to the extracted watermark; and
an inhibitor configured for preventing playback of the digital data stream when the hashed ticket does not match the extracted watermark.
These and other aspects, features and advantages of the present invention will become apparent from the following detailed description of preferred embodiments, which is to be read in connection with the accompanying drawings.